System and method for sparse touch sensing on capacitive touch screen

Abstract

An embodiment of the invention provides a method of detecting the position(s) where sensor(s) are activated on an interactive screen using sparse-activation compressive sensing. Sparse-activation compressive sensing makes use of the situation where the number of simultaneously activated sensors is substantially smaller than the number of sensors (nodes). Because the number of simultaneously activated sensors is substantially smaller than the number of sensors, the number of measurements required for determining which sensors are activated may also be reduced. Because fewer measurements are required when compared with full-scan techniques, less circuitry and power is required to detect the location(s) of activated sensors on an interactive screen.

What is claimed is: 
     
       1. A non-transitory machine-implemented method of determining where activated capacitance sensors are located on a capacitive-touch interactive screen comprising:
 a first step, the first step comprising:
 precharging each capacitance sensor in a group of N capacitance sensors to a distinct voltage V n ; 
 electrically connecting all N capacitance sensors in parallel; 
 transferring charge from all N sensors connected in parallel to a reference capacitor C ref ; 
 converting the charge transferred to the reference capacitor C ref  to a sensed voltage V sense ; wherein the sensed voltage V sense  equals a single state; storing the single state; 
 
 a second step, the second step comprising:
 repeating the first step K times; wherein the value of K is substantially less than the number of sensors N; 
 
 a third step, the third step comprising:
 determining a capacitance C n  for each capacitance sensor in the column of N capacitance sensors by solving an equation using sparse-activation compressive sensing, the equation given by: 
 
 
       
         
           
             
               
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         wherein C m,n  is the node capacitance of a capacitance sensor at the intersection of row m and column n; wherein m=(0, 1. . . , M−1); 
         wherein an activated capacitance sensor on the capacitive-touch interactive screen is located where the capacitance C m,n  of sensor (s) is different from the capacitance of capacitance sensors that are not activated on the capacitive-touch interactive screen. 
       
     
     
       2. The non-transitory machine-implemented method of determining where activated capacitance sensors are located on the capacitive-touch interactive screen of  claim 1  wherein parasitic capacitance of the N sensors in the column is given by:
       c     n   =[  C     0,n    . . .  C     M−1,n ] T    
 wherein change in capacitance at a sensor is given by:
   Δ c   n   =c   n   −  c     n 
 
 
 wherein the number of non-zero values for ΔC n  is substantially fewer than the number of N sensors; 
 wherein a calibrated voltage v n   c  is equal to:
     v   n   c =Φ n   Δc   n   +e   n  
 
 
 wherein e n  is calibration error; 
 wherein ΔC n  is determined by solving the following equation:
   min∥Δ c   n ∥
 
   such that 
     ∥v   n   c −Φ n   Δc   n ∥≦∈
 
 
 wherein ΔC n  has a sparsity s with K=O(s*log(M/s)).